Determination of the Beta-Decay Interaction From Electron-Neutrino Angular Correlation Experiments

Authors(s):James S. Allen Publication:Reviews of Modern Physics Publication Date:July 1, 1959 Publisher: Citation:RevModPhys.31.791 Link:

The methods used to obtain a series of measurements of the angular correlations in the allowed beta decay of described. Schematic diagrams of the apparatus used in various experiments are given. The results prove that the dominant interactions are vector for the Fermi type of decay and axial-vector for the Gamow-Teller decays with the dominant interaction form being VA. The present experiments do not exclude a possible tensor admixture of 10% or less. A scalar mixture of the same magnitude may also be present. (C.J.G.)

Experimental determination of the specific form of the interactions responsible for nuclear beta decay has remained a critical problem ever since the original formulation of the theory by Fermi. ' Bloch and Moiler' probably were the first to point out that the electron-neutrino angular correlation in nuclear beta decay depends on the type of lightparticle-neutron interaction assumed in the Fermi theory. According to present ideas, a linear combination of five relativistically invariant expressions can be chosen for the interaction Hamiltonian. The individual interactions are the scalar, vector, tensor, axial-vector, and pseudoscalar interactions, denoted respectively S, V, T, A, and E. In the case of allowed transitions, the pseudoscalr interaction usually is small compared to the other forms and can be omitted.